1. Field of the Invention
This invention relates generally to a shelf assembly of an electronic apparatus such as a communication apparatus, and more particularly to a mounting structure of a back wiring board to a shelf.
2. Description of the Related Art
There is a tendency that a demand for mounting electronic devices and equipment, such as communication devices, in high density. Usually, a vertical mounting of a printed wiring board is employed. In a vertical mounting of a printed wiring board of a communication device, electronic circuit packages each including a printed wiring board, on which a plurality of electronic parts such as LSI having an electronic circuit formed thereon are mounted as one group, are received in a shelf with their vertical postures, each electronic circuit package is connected to a back wiring board provided on a rear side of the shelf, with the use of a connector, thereby constituting a shelf unit. A loading of a plurality of such shelf units onto a rack completes a constitution of a communication device.
A conventional method for mounting a back wiring board to a shelf generally employs a way for mounting a back wiring board to a shelf from a rear side of the shelf and securing the back wiring board to the shelf by screws which are screwed into a rear surface of the back wiring board. However, this mounting method is practically impossible to apply to a local station electronic switch board which employs a rear surface mating structure of a rack, because only a front surface maintenance can be made. In order to make it possible to perform a variety of maintenance works of a back wiring board from the front side, there is known another mounting method in which a back wiring board is screwed tight to a back-board mounting frame and the back-board mounting frame is screwed tight to a shelf from a front side of the shelf.
According to the second-mentioned mounting method, it is sure that the front surface maintenance of the back wiring board is improved. However, since the back wiring board is screwed tight to the back-board mounting frame, many working processes are required. Moreover, the back-board mounting frame, which is employed in this mounting method, has the shortcomings in that a structure thereof is complicated and a weight thereof is heavy.
A press hit pin, which is inserted in the back wiring board, is allowed to project from the rear surface side in order to facilitate a jumper connection to be made on the rear surface side of the back wiring board. Therefore, when the back wiring board is placed directly on the floor, there is a fear that the pin is bent to form a short circuit with its adjacent pin. In order to prevent this, it is desirable from a view point of reliability to employ a back-board mounting frame. The conventional back-board mounting frame structure is complicated because it employs a mounting method in which the back wiring board is laid over the back-board mounting frame.